In recent years, a digital copying machine has various functions for processing a document image, such as black-and-white inversion, mirroring, inside-blanking, or image separation. Furthermore a color digital copying machine has, in addition to the functions described above, color processing functions such as color conversion or color deletion. A user selects a desired image area or any one of the functions described above for a particular image from an operating section or with an editor to set conditions for image processing. In this case, generally, a user outputs a trial copy to check whether a desired image quality can be obtained or not, executes fine adjustment in a case where a desired image quality has not been obtained, and again outputs a trial copy for checking finishing of the outputted copy.
Also there has been known an apparatus in which functions for .gamma.-correction (density conversion) for subjecting various types of document image including a diagram comprising lines such as a character image, an image in which gray levels indicates information such as a color map to density correction with a processing suited to each type of image are provided and a user can select any of the functions.
Also in the conventional type of copying machine, separation of a character section, a screen tone section, and a photograph section which coexists in a document image has been executed, for instance, by screen tone separation by means of edge detection and pattern matching according to a degree of contrast in each area of the image, and furthermore a high image quality has been realized by way of automatically executing an optimal gray level processing or a filtering such as a character mode or a photograph mode.
Also in order to eliminate the necessity for the trial copying works as described above, as an image forming apparatus in which a user executes image processing for a read image as an object for recording checking displays provided on the monitor and records the image after having been subjected to the image processing, the "image processing system" disclosed in Japanese Patent Laid-Open Publication No. 288467/1990 has been known.
Also as one of the related referential technological documents, a "digital copying machine" is disclosed in Japanese Patent Laid-Open Publication No. 68161/1993. This digital copying machine has functions for taking out a required portion from a displayed image, allocating it at a necessary point, and synthesizing a plurality of images, and outputs a new image.
In the conventional type of copying machine as described above, however, in a case where a desired image is obtained by using each image editorial function, as images in two state, namely am image prior to processing and that after processing can not be outputted on a screen simultaneously, so that it has been disadvantageously impossible to efficiently and accurately confirm how a result of image processing is.
The problems relating to the conventional technology can be summarized as follows.
Firstly, when a user selects parameters for image processing, a relation between an image prior to processing and that after processing can not directly be confirmed in its adjustment, so that operations for fine adjustment are difficult.
Secondly, in a case where parameter setting is executed in the form of fine adjustment, a required image quality is extremely high, so that there is no way but to confirm a result of adjustment by outputting a trial copy, which makes the workability lower with the operating cost increased.
Thirdly, as the .gamma.-characteristics of a read image or those of an output image can not be determined previously, density adjustment for an output image in response to the document image can not accurately be executed.
Fourthly, in operations for recognizing each area when separating specific areas of an image and for setting conditions for the processing, a portion of the processing for image separation can not be executed in good conditions due to a state of a document image, and optimal conditions can not be set, which makes lower not only the image quality but also efficiency in operations for setting conditions for the processing.